gatsby-source-contentful returns empty srcSet and srcSetWebp when querying fixed images with only height argument.

[mrseanbaines]

Description

gatsby-source-contentful returns empty srcSet and srcSetWebp when querying fixed images with only height argument.

These values are included when making the same query but passing in a width argument, and also included when passing a height argument if using gatsby-plugin-sharp. See screenshot for comparison:

Steps to reproduce

1. Create new Gatsby project from default starter
2. Install and configure gatsby-source-contentful
3. Upload gatsby-astronaut image to Contentful
4. Edit the Image component query to this:

query {
  contentfulAsset(title: { eq: "gatsby-astronaut" }) {
    fixed(width: 500) {
      width
      height
      src
      srcSet
      srcWebp
      srcSetWebp
    }
  }
}

Expected result

A value for both srcSet and srcSetWebp should be returned.

Actual result

Empty strings are returned for both fields.

Environment

  System:
    OS: macOS 10.15.4
    CPU: (8) x64 Intel(R) Core(TM) i5-8279U CPU @ 2.40GHz
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 12.16.1 - /usr/local/bin/node
    Yarn: 1.22.4 - ~/.yarn/bin/yarn
    npm: 6.13.4 - /usr/local/bin/npm
  Languages:
    Python: 2.7.16 - /usr/bin/python
  Browsers:
    Chrome: 83.0.4103.61
    Firefox: 76.0.1
    Safari: 13.1
  npmPackages:
    gatsby: ^2.21.37 => 2.22.9 
    gatsby-image: ^2.4.4 => 2.4.4 
    gatsby-plugin-manifest: ^2.4.5 => 2.4.9 
    gatsby-plugin-offline: ^3.2.3 => 3.2.7 
    gatsby-plugin-react-helmet: ^3.3.1 => 3.3.1 
    gatsby-plugin-sharp: ^2.6.4 => 2.6.9 
    gatsby-source-contentful: ^2.3.12 => 2.3.12 
    gatsby-source-filesystem: ^2.3.4 => 2.3.8 
    gatsby-transformer-sharp: ^2.5.2 => 2.5.2